If you use the mem_cache_store it will use “memcache-client” to talk to
the actual cache.
memcache-client is a pure Ruby library that is bundled with rails. There
is a Ruby/C library called “memcached” that uses native bindings to
talk to memcache, and it is reportedly (http://blog.evanweaver.com/files/doc/fauna/memcached/files/README.html)
up to a 100 times faster than memcache-client. To use that instead,

# in shell$ sudogeminstallmemcached--no-rdoc--no-ri# in config/production.rbrequire'memcached'config.action_controller.cache_store=:mem_cache_store,Memcached::Rails.new("localhost:11211")

This feature (to pass a configured MemCache-like object to cache_store=)
is available since rails 2.3.3 and will hopefully be documented in 2.3.5.